Expand and combine like terms. $(4b^2+3)(4b^2-3)=$
We can expand this expression like any product of two binomials. However, this expression has a special form that makes it easier to expand. This is the "difference of squares" form (where $P$ and $Q$ can be any monomial): $(P+Q)(P-Q)=P^2-Q^2$ $\begin{aligned} &\phantom{=}(4b^2+3)(4b^2-3) \\\\ &=\left(4b^2\right)^2-(3)^2 \\\\ &=16b^4-9 \end{aligned}$